This invention relates to valve assemblies and, more particularly, to spool-type valve assemblies having a plurality of valve lands slidably disposed in a valve bore.
Spool valve assemblies are generally comprised of a slidable valve spool, a valve bore and a control spring or bias spring. The valve spool has a plurality of lands which are disposed slidably within the valve bore and in sufficiently close tolerance to inhibit leakage past the valve land while controlling fluid flow between fluid ports connected with the valve bore. The valve spool generally has a leading valve land, which inserts into the bore first during assembly and is susceptible to burrs and other damage during handling if proper handling precautions are not employed. A burr on the leading edge can disturb the valve operation as well as disturb the clearance between the valve bore and the valve land by scratching or otherwise marring the valve bore during forced insertion by an operator or assembler. Also, a slight nick or burr on the leading valve land can result in misoperation of the valve and that the return spring does not have sufficient force to move the valve to the proper location within the valve bore when the control pressures are not existent.
This problem is generally disclosed or found by misoperation or nonoperation of the device controlled by the valve spool or valve assembly. Generally, this misoperation is sensed in the inadequate exhausting of a fluid clutch or brake in a transmission or the inability of a clutch or brake to be applied. Also, if the valve is a pressure regulating-type valve, the improper regulating pressure may be present within the system due to the marring of the leading edge of the valve.
It is an object of the present invention to provide an improved valve assembly wherein the valve spool has a leading edge, which is sufficiently small to not contact the valve bore during assembly.
In one aspect of the present invention, the leading end of the valve spool has a bore that is slightly smaller in diameter than the leading edge of the control portion of the valve spool found on the first land.
In another aspect of this present invention, a recess is formed between the leading or pilot end of the valve spool and the leading end of the sealing land such that any debris present at assembly will be dislodged into the recess and exhausted from the valve by fluid flow through the valve.